Disclaimer: Is there anyone who doesn't know that… J.K. Rowling owns Harry Potter. I do not.
The house itself seemed to shake as he slammed the door behind him. He refused to even look back, though. He hoped it would fall to the ground in ruins. He was never going back there. Never. He'd never belonged there, and now he knew for sure that he never would. Unfortunately, though, he couldn't apparate to James's house. One more year, and he'd be able to, but for now, he was still on holiday from Hogwarts, and he was also still 16. Muggle transportation it would have to be.
As Sirius sat on the underground and watched the stops rattle by, he surreptitiously felt for his wand in his back pocket. Once sure it was there, he stared straight ahead at his reflection in the window. The people sitting across from him were trying not to look at him too curiously, but he knew they'd been staring. He didn't exactly blame them. He looked a sight, for sure, with his hair in disarray and his rattiest clothes. He'd worn them to anger his mother although she clearly thought his clothes were the least of her problems. Running away really was the only option. She would never understand. His lips twisted in a wry smile when he thought of what her reaction would be when she found out he was staying at the Potters. She'd never known what to make of them… pure bloods who DIDN'T side with the "Dark Lord," as she liked to call him.
By the time he got to a stop close enough to James's house, he was half asleep and had to shake himself awake. Climbing up the steps into the fresher air, he felt once more for his wand and then trudged the well-known path to James's house. He wished he'd been quick enough to grab the floo powder to save himself this trek, but he knew he couldn't have stayed in that house a moment longer. He shook himself as though he were a dog, trying to rid himself of fleas as he tried to shake all of the negativity off him as he approached his best friend's house. A dog… he couldn't help but smile. If only he'd been able to become Padfoot for this journey… it wouldn't have been such an uncomfortable experience on the Underground. But he and his fellow Marauders were lucky enough not to get caught at Hogwarts with their unregistered animagi, so they were even more careful not to test those waters at home.
Finally, the house was in sight, and Sirius felt himself starting to relax as he walked up the worn pathway nestled between neatly trimmed hedges. It couldn't have been more different from the dark house he was leaving behind. Dark in more ways than one, he thought, his lips twisting bitterly as he reached up to use the knocker in the center of the bright red door. Happily for him, James answered the door. He looked glad to see Sirius … but very confused. Sirius couldn't blame him. He'd shown up sort of unexpectedly before but there had usually been some kind of notice involved.
"Come – come in," James said, recovering from his momentary surprise with as much grace as possible.
"Thanks, mate," Sirius said, clapping him on the shoulder as he stepped into the entryway that had always felt more like home than Grimmauld Place. Looking around, he let out another deep breath.
I'm going to be ok, he thought to himself. I'm with the Potters now. No one back there will even notice I'm gone.
At this last thought, Sirius was horrified to realize there was a lump in his throat. This was ridiculous. He was happy to be out of there. Nothing good could come of staying at his parents' house. He swallowed hard and forced a grin.
"Got something to eat?" he asked James, who nodded agreeably and led the way into the kitchen. His parents were sitting at the table when the boys walked in, and Katherine Potter looked up, smiling when she saw Sirius enter the room.
"Oh, it's good to see you again, dear. James didn't mention you were coming. Would you like to stay the night?"
Sirius nodded, grinning at her, wondering why this smile suddenly hurt. "Thanks, Mrs. Potter. That'd be great."
There would be time later to tell James what had happened. He could tell his parents. Then they'd all figure out where he'd stay. This was going to work out. It had to.